Cutting apparatus for making finely controlled cuts utilizing a tiltable wheel for regulating the cutting blade movement

ABSTRACT

A cutting apparatus including a closed-loop saw blade extending around a portion of the periphery of a rotatable and tiltably mounted control wheel is disclosed. The blade is driven by a drive wheel and rotates the control wheel about its axis. The blade is moved in a cutting direction parallel to the plane of the blade by tilting the control wheel, the tilting motion providing very accurate control of the cutting depth of the blade. The blade is tensioned by a third wheel.

United States Patent William S. Phy

Los Altos Hills, Calif.

Sept. 2, 1969 Aug. 17, 1971 Fairchild Camera and Instruments Corporation Mountain View, Calif.

Inventor Appl. No. Filed Patented Assignee CUTTING APPARATUS FOR MAKING FINELY CONTROLLED CUTS UTILIZING A TILTABLE WI-IEEL FOR REGULATING THE CUTTING BLADE MOVEMENT 1 Claim, 4 Drawing Figs.

US. Cl Int. Cl

125/21 B28d l/08 Field of Search 51/135 BT; 125/21;83/201.04;143/31 References Cited UNITED STATES PATENTS 1/1969 Cleland 286,919 10/1883 Friedli 143/31 2,803,239 8/1957 DAvaucourt 125/21 2,431,795 12/1947 Elmes 51/135 UX 779,158 l/1905 l-larrold.. 143/31 120,949 11/1871 Doane.... 143/31 X 2,369,068 2/1945 Mentzer 125/21 FOREIGN PATENTS 538 2/1878 Great Britain 125/21 Primary Examiner-Harold D. Whitehead AtlorneysRoger S. Borovoy and Alan H. MacPherson ABSTRACT: A cutting apparatus including a closed-loop saw blade extending around a portion of the periphery of a rotatable and tiltably mounted control wheel is disclosed. The blade is driven by a drive wheel and rotates the control wheel about its axis. The blade is moved in a cutting direction parallel to the plane of the blade by tilting the control wheel, the tilting motion providing very accurate control of the cutting depth of the blade. The blade is tensioned by a third wheel.

PATENTEI] AUG] 1197:

FIG.|

v INVENTOR. WILLIAM S. PHY

m /v y/ W ATTORNEY v CUTTING APPARATUS FOR MAKING FINELY CONTROLLED CUTS UTILIZING A TILTABLE WHEEL FOR REGULATING TI-IE CUTTING BLADE MOVEMENT BACKGROUND AND BRIEF SUMMARY OF THE I INVENTION In the manufacture of semiconductor devices, a plurality of separate devices are formed on a single wafer and arranged in multiple columns and-rows. After formation, the individual devices are separated or diced from the wafer for subsequent use, the defective die being discarded. Separation of the in? dividualdice is generally accomplished by first scribing the wafer between the rows and the columns and by then breaking the die off into their individual form.

This scribe-and-break technique is not satisfactory in all cases, and in particular in those instances where the die are either very small or very large. Certain semiconductor devices are made with as many as 100 columns and rows on a single chip with the individual devices 6 mil square, It is very difficult to scribe and break a chip into such small die. On the other hand, it has been found difl'icult to properly dice semiconductors such as large area calibration diodes made of silicon and with dimensions up to one-quarter inch square by the scribing method.

In addition, the scribe-and-break process is not appropriate where the material of the semiconductor wafer is friable, as is the case, for example, with gallium arsenide and gallium phosphide; Also, there are instances where the wafers are scarce or are relatively expensive and the scribe-and-break technique, although generally satisfactory, is too much of arisk under such circumstances. I

' For those instances where the scribing technique is not appropriate, cutting or sawing has been employed to separate the individual die from the chip. One common form of saw employs a clo e wire loop which passes through an abrasive slurry, the wire being urged against the object to be cut by a dead; weight system 'or by a positive drive which may, for example, be hydraulically operated. These wire band systems are generally slow cutting, taking up to to minutes to make a 6. mil cut in a silicon wafer. In addition, the wire loop doesnot have good lateral stability and it tends to move sideways as it cuts. As a result, the cut produced willnotbe straight or normal to the surface. Alsofthe abrasive slurry surrounding the fastmoving tends to widen the cut opening above the wire, thus resulting in a cut which is wider at the top than at the bottom.

Another; form of saw utilizes a reciprocating blade which is urged by a positive drive against the object to be cut. This reciprocating blade does, not track well; the blade, after moving in one direction, does not return precisely along the same line of travel when moving in. the opposite direction and the resultant cut is much wider than desired. In addition, reciprocating mechanisms are. not satisfactory for use with frangible objects because the side shocks produced during reversal of theblade result inv a crumbling of the sides of the cut.

Systems, have alsobeen usedwhere the object is moved into the saw blade. he cut being controlled by controlling movement of the object by precise mechanisms, such as pneumatic drive systems. These systems are complex and expensive.

The object of; the present invention is to provide a fast accurate, and. economical, cutting apparatus and, more particularly, to provide a cutting apparatus which will make very well-defined cuts normal; tot-hecuttingsurface and with accurately controlled, depths, such. apparatus, being useful, for example, in thedicing ofa semiconductor wafer.

The cutting apparatus of the present. invention includes a saw blade-comprising a thin band-which is formed ina closed loop, oneedge of the thin band serving as. the cutting edge. Theband passesaround a portion-of the periphery of a drive wheeliwhichservesto-drive the-bandin a linear direction past a. region in-whichan object such as a; silicon wafer is positioned for cutting. The cutting edged the band'passes at a high rate of speed over and narrowly spaced from the surface of the object to be cut.

The band passes around a portion of the periphery of a con- 5 tro] wheel, the control wheel being rotatably mounted so as to rotate about the normal axis which extends perpendicular to the plane of thewheel and through its center, i.e., the hub of the wheel, the peripheral surface of the control wheel contacting and moving with the cutting band. Means is provided for producing a suitable tension in the fast-moving cutting band.

The control wheel is mounted on a yoke structure so as to be tiltable about an axis perpendicular to its normal axis, tilting of the control wheel causing the cutting band to move in a direction parallel to its surface and bring the cutting edge into contact with the surface of the object to be cut. Progressive tilting of the control wheel causes the cutting blade to cut into the object, the degree of tilt controlling the depth of the cut.

. The lever action of the control wheel and yoke provide accurate depth control of the cutting blade.

For cutting hard objects such as silicon semiconductor wafers, the cutting band is a strong flexible material such as beryllium copper formed with a cutting edge of diamond powder plated in a nickel matrix and traveling at speeds from 100 to 1,500 feet per minute.

These and other features and advantages of the present invention will become more apparent upon perusal of the following description taken in connection with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the novel cutting apparatus of the present invention,

FIG. 2 is a cross section view taken through section line 2-2 in FIG. I showing the control wheel of this novel cutting apparatus,

FIG. 3 is a cross section view showing the cutting blade and the object being cut and taken through section line 3-3 in FIG, 1, and I FIG. 4 is a cross section view showing the control wheel in a tilted position and taken along section line 4-4 in FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION Referring now to the drawings, the cutting apparatus comprises a closed loop band 11 made of suitable metallic material such as beryllium copper one-quarter inch wide and a few mils thick. The lower edge 12 of the band carries diamond powder plated into a nickel matrix and serves as a cutting edge. If desired, the upper edge 13 may also be plated with diamond powder so that the blade is reversible.

The blade passes around a portion of the periphery of a drive wheel 14 fixedly secured on shaft 15 which is driven by an electric motor 16 and pulley 16. The electric motor is mounted on, the underside of a main baseplate 17, the shaft 15 extending up through the plate to hold the drive wheel spaced slightly above the plate.

A tension wheel I8 is rotatably mounted on a shaft 19 carried by a slide member 21', the member 21 being slidably mounted on two rods 22 which are fixedly secured within an opening 23 in the baseplate 17. A screw 24 is mounted in the plate 17 and extends into the opening 23 where it is threaded into the slide member 21. Two compression springs 25 extend over the tworods 22 and between one edge of the opening 23 inrthe-baseplate 17 and the slide member 21.

A U-shaped yoke 26 is pivotally mounted at its two side legs by pivot, pins 27 on two bearing members 28 extending from the upper surface of the baseplate 17. The yoke is positioned in an opening 29 in the plate and carries a shaft 31 which is fixedly secured in the center of the yoke. The shaft 31 extends above and below the base 26' of the yoke, a control wheel 32 being rotatably mounted on the upper end of the shaft 31. An adjusting rod 33 coupledto and driven by a micrometer screw face of the plate 17, the free end of the rod abutting against the lower end of the shaft 31. The lower end of the shaft 31 is also coupled to one end of a tension spring 34', the other end of spring 34' being connected to the support member 35.

The blade 11 extends around the drive wheel 14, the tension wheel 18 and the control wheel 32, and passes over two idler wheels 36 and 37 rotatably mounted on the baseplate and positioned between the control and drive wheels. The peripheral surfaces of the wheels are made of a high-friction material such as hard rubber with good wear characteristics. A high-tensile stress such as 50 percent of the tensile strength of the material, for example, 50,000 psi. for beryllium copper, is established in the band 11 by drawing the slide member 21 and tension wheel 18 up against the compression springs 25 on the slide rods 22 with the tension adjust screw 24. The tensioned saw blade or band 11 exerts a force on he control wheel 32; however, this force is not sufficient to overcome the force of tension spring 34' whichurges the shaft 31 against the end of the adjusting rod 33; In the normal at rest position, the shaft 31 is positioned normal to the surface of the plate 17, control wheel 32 being parallel to plate 17.

The object to be cut, which may, for example, be a silicon semiconductor wafer 38 having a plurality of separate devices formed in columns and rows thereon, is positioned and held on a vacuum chuck 39 within an elongated opening 41 in the plate 17 between the two idler wheels 36, 37. The chuck 39 is supported by a table 42 arranged to move the chuck to the right or left as viewed in FIG. 1 (the X direction) by means of a micrometer screw device 42' to center the wafer 38 in the opening 41 and also move the wafer toward the top or bottom of FIG. 1 (the Y direction) by means of another micrometer screw device 43 to position the wafer for cutting by the blade lLThe table is also provided with means including micrometer screw 44 for rotating the chuck 38 to align the rows of semiconductor devices on the wafer with the blade 11 extending between the two idler wheels 36 and 37 and to also rotate the chuck 90 when desired to align the columns of devices on the wafer with the blade 11. Provision is also made to raise and lower the table 42 to properly space the wafer from the cutting edge 12 ofthe blade 1 l.

In operation, the drive wheel 14 drives the blade 11 between the two idler wheels 36 and 37 at selected speeds between 100 to 1,500 ft./min., preferably 1,000 ft./min. The

blade edge 12 is brought into cutting engagement with the wafer 38 by turning the micrometer screw 34 to extend rod 33 and move the lower end of shaft 31 to the right as viewed in FIG. 4. The yoke 26 is pivoted on pins 27 and tilts the control wheel 32 about an axis which extends through the axis of the I 34 is carried on a support member 35 secured to the undersurtwo pin 27, the wheel 32 being mounted on shaft 31 in such, a manner that the tilting axis lies along a diameter of the wheel 32. In tilting, the control wheel lowers the portion of the band 11 passing over its periphery, which in turn causes the band passing between the idler wheels to be lowered into engagement with the wafer 38. Continued movement of rod 33 and tilting of the control wheel 32 moves the cutting edge 12 of the band 11 into and through the wafer. The band 11 travels in a very straight line between the two idler wheels 36 and 37 and produces a straight, narrow cut in the wafer. The depth of the cut may be very accurately controlled by the screw 34, the speed of the blade and the cutting force giving a rate of cutting of about 1 mil/sec. for a 2 inch length of cut. The depth of cut ranges to 50 mils or greater. A stream of water (not shown) is directed on the blade near the cutting region to cool the blade and remove residue.

When the micrometer screw 34 and rod 33 are retracted the shaft 31 returns to its normal, upright position under the urging of spring 34', the control wheel 32 returning parallel to the surface of plate 17 and raising the blade 11 up out of the water It should be noted than although the present improved band saw was described with reference to the dicing of semiconductor wafers, the improved structure is suitable for use with band saws in general where high speed, accurate cuts, and controlled cut depths are desirable. It should also be noted that automatically operated stepping means could be utilized in place of the micrometer screws 42' and 43 to position the wafer 38 for cutting and an automatically operated motorized cam mechanism utilized to periodically tilt the control wheel to produce the spaced-apart cuts in the wafer.

What I claim is:

1. A cutting apparatus comprising a closed metallic band having a continuous cutting edge, three spaced-apart rotatable wheels, the band passing over and contacting portions of the peripheral surface of each wheel, means for driving one of said wheels to move said band in a path encompassing said three wheels, means for moving a second one of said wheels against said band to produce a tension therein, said band moving in a linear direction between one of said first and second wheels and said third wheel and through a stationary cutting region, a yoke tiltable about an axis, means mounting said third wheel to rotate about its axis on said yoke and in the plane of said yoke axis, means extending from said yoke and along said 'wheel axis and screw means abutting said extending means for tilting said third wheel to move said band within said cutting region in a direction perpendicular to said linear direction and parallel to the plane of the band. 

1. A cutting apparatus comprising a closed metallic band having a continuous cutting edge, three spaced-apart rotatable wheels, the band passing over and contacting portions of the peripheral surface of each wheel, means for driving one of said wheels to move said band in a path encompassing said three wheels, means for moving a second one of said wheels against said band to produce a tension therein, said band moving in a linear direction between one of said first and second wheels and said third wheel and through a stationary cutting region, a yoke tiltable about an axis, means mounting said third wheel to rotate about its axis on said yoke and in the plane of said yoke axis, means extending from said yoke and along said wheel axis and screw means abutting said extending means for tilting said third wheel to move said band within said cutting region in a direction perpendicular to said linear direction and parallel to the plane of the band. 